ENZYMES

Reactions are catalysed by enzymes.

Biological catalysts

Globular proteins that interact with substrate molecules causing them to react at much faster rates without the need for harsh environmental conditions.

Chemical reactions required for growth are anabolic and they are are all catalysed by enzymes

In metabolic pathways consisting of many catabolic reactions, energy is released from large organic, like glucose.

Reactions rarely happen in isolation but as part of multi-step pathways. Metabolism is the sum of all different reactions and reaction pathways happening in a cell or an organism.

Speed of reactions varies and is usually dependant on environmental conditions.

Enzymes can only increase the rates of reaction up to a certain point called the Vmax 

Molecules in a solution move and collide randomly. Molecules need to collide in the right orientation.

Many different enzymes are produced by living organisms. Each enzyme catalyses one biochemical reaction of which there are thousands in any given cell called the specificity of the enzyme.

Activation energy - energy needed to be supplied for the reaction to start.

Enzymes help molecules to collide reducing the activation energy.

An area within the tertiary structure of the enzyme has a shape that is complementary to the shape of a specific substrate molecule called the active site.

Only a specific substrate will fit the active site of an enzyme.

An enzyme-substrate complex is formed when the substrate is bound to the active site. 

They react and products are formed in an enzyme-product complex 

The products are released leaving the enzyme unchanged to take part in subsequent reactions.

The substrate is held so the right atom-groups are close enough to react. The R-groups within the active site of the enzyme will interact with the substrate forming temporary bonds putting a strain on the bonds within the substrate speeding the reaction

Active site of the enzyme changes shape slightly as the substrate enters.

The initial reaction between the enzyme and the substrate is relatively weak but rapidly induce changes in the enzyme's tertiary structure strengthening binding, putting strain on the substrate molecule.

Weaken a particular bond or bonds in the substrate lowering the activation energy.

Enzymes that act within cells.

Hydrogen peroxide is a toxic product

Work outside the cell.

Raw materials need to be constantly supplied and are found in the diet in the form of proteins and polysaccharides. These are too large to enter the cell-surface membrane. 

Begins in the mouth and continues in the small intestine.

1. Starch polymers are partially broken down into maltose (disaccharide) by amylase which is produced by the salivary glands and pancreas

2. Maltose is broken down into glucose (monosaccharide) by maltase which is present in the small intestine

Trypsin is a protease that catalyses the digestion of proteins into smaller peptides which can be broken down further into amino acids by other proteases.

Trypsin is produced in the pancreas and released with the pancreatic juice into the small intestine.

Amino acids that are produced are absorbed by the cells lining the digestive system and then absorbed into the bloodstream

Enzymes are activated with cofactors or inactivated with inhibitors.

Inhibitors are molecules that prevent enzymes from carrying out their normal function of catalysis.

A molecule or part of a molecule that has a similar shape to the substrate of an enzyme can fit into the active site of the enzyme 

Blocks the substrate from entering the active site.

The enzyme cannot carry out its function 

Degree of inhibition will depend on the relative concentrations of substrate, inhibitor and enzyme.

Statins inhibit the enzyme used in the synthesis of cholesterol.

Inhibitor binds to the enzyme at the allosteric site changing the enzymes tertiary structure which means the active site changes shape.

Active site no longer has a complementary shape to the substrate.

Increasing the concentration of enzyme or substrate will not overcome the effect of a non-competitive inhibitor. Increasing the concentration of inhibitor will decrease the rate of reaction further.

Binding of the inhibitor may be reversible or non-reversible.

Product of a reaction acts as an inhibitor to the enzyme that produces it.

Serves as a negative feedback control mechanism for the reaction.

Excess products are not made and resources not wasted.

Example of non-competitive reversible inhibition 

Cofactors may transfer atoms or groups from one reaction to another in a multi-step pathway or may actually form part of the active site of an enzyme.

If the cofactor is an organic molecule it is called a coenzyme.

Many coenzymes are derived from vitamins.

Tightly bound and form a permanent feature of the protein

They are cofactors

Many enzymes are produced in an inactive form, known as inactive precursor enzymes.

Often undergo a change in shape, particularly to the active site to be activated which can be achieved by the addition of a cofactor.

Before the cofactor is added the precursor protein is called an apoenzyme.

When the enzyme is added and the enzyme is activated, it is called a holoenzyme